Amazing Benefits of High-Intensity Exercise

By Jes Williams @feelmoregooder

High-intensity exercise, like many fitness trends, has gained both good and bad popularity in the health world. Some tout high-intensity exercise (also commonly referred to as HIIT) as an excellent addition to any routine, one that enhances your metabolic function and helps you burn excess adipose (fat) tissue. Other voices in the functional medicine world are weary of high-intensity exercise, warning that it negatively spikes cortisol.

Something that we an all universally agree upon is that you can absolutely overdo something to the point that it is detrimental. Perhaps, a healthy seeking of a harmonious, balanced relationship to exercise is what we ought to be after. Additionally, like many topics under the health umbrella, it is not always one-size-fits-all. 

However, it can be helpful to guide the helm back to the science and what the literature reveals in terms of the verdict pertaining to HIIT. This, coupled with our own personal history and experience will guide you towards an individualized approach that can best suit you.

Risk Factors and History of Exercise

Knowing the stats & risk factors can be a helpful motivator for some. Also, it’s important to know there is a lot you can do to lower your risk. Lifestyle choices like what your nutritional profile looks like and how active you are play big roles in moving on the needle on your personal risk. Fortunately, these are within your control. With some modifications, you can improve your days to cater to your optimal health.

Exercise has been a foundational aspect of any prevention plan by physicians for centuries, with documentation referencing back to around 460 B.C. to 377 B.C, when Hippocrates, The Father of Medicine, lived and practiced. He is quoted saying “Walking is man’s best medicine” and “if there is a deficiency in food and exercise, the body will fall sick (2,3). In addition to exercise in general being positively correlated with health state, HIIT specifically is a healthful modality to integrate, too.

"High-intensity interval training (HIIT) refers to exercise that is characterized by relatively short bursts of vigorous activity, interspersed by periods of rest or low-intensity exercise for recovery."

PMID: 23899754 (4)

High-Intensity Exercise for Cardiovascular Health

According to the CDC, heart disease is the leading cause of death in the United States for both women and men. Additionally, cardiovascular disease is also the leading cause of death globally, responsible for about 17.9 million deaths per year. (1) Studies suggest that aerobic capacity is the strongest predictor of future health, all-cause mortality, and overall cardiovascular risk. We discuss later in this post how your VO2 max & aerobic capacity is improved by including HIIT training in your routine. Therefore, it's advantageous to include high-intensity exercise even if youre only focus is heart health.

High-intensity interval training is recognized as a more efficient protocol than moderate-intensity continuous training (MCT). In other words, doing a 30-minute workout comprised of 1 minute of work alternating with 1 minute of resting is more beneficial than doing 30 minutes of static-pace continuous work. (7) The interesting reality is that even though the benefits of sufficient exercise (and HIIT, specifically) are well established in the literature, the World Health Organization still estimates that about 27.5% of the population in 2016 was recognized as sedentary, meaning they exhibit insufficient physical activity.

"It is well documented that HIIT provides a robust stimulus for central cardiovascular adaptations and metabolic stress."

PMID  34281138, referencing PMID: 23899754

HIIT for Metabolic Health

Put simply, regularly including high-intensity interval training into your weeks will help to boost your metabolism. In other words, you may experience healthy weight loss and a reduction in adipose tissue. It's key to pay attention to what works best for you when considering a frequency and training schedule.

Moreover, HIIT has been observed a highly effective stimulus to improve anaerobic metabolism. Though this is clearly helpful for anyone, the use of HIIT training with the obese, overweight, and primarily sedentary individuals can be especially helpful. Another interesting component of the research on the link between HIIT & metabolic health is that it was found that "the detrimental effects of sleep loss on glucose metabolism and mitochondrial functions and glucose tolerance can be overcome by performing a single bout of high-intensity interval exercise." It's fascinating that you can help mitigate the negative side of suboptimal life choices of sleep neglect (and dysregulated blood sugar) by implementing HIIT. It serves as a powerful reminder that the benefits of exercise far surpass any aesthetic goals surrounding physical fitness.

"Research has indicated that high-intensity interval training induces numerous physiological adaptations that improve exercise capacity (maximal oxygen uptake, aerobic endurance, anaerobic capacity etc.) and metabolic health."

PMID: 34281138

HIIT for Enhancing Endurance Capacity

Fitness capacity can be broken down into three different categories based on energy systems: glycolytic (think 1 rep max, sprints, full and fast effort), phosphagen (mid-rep range, movement that takes place between 10-30 seconds), and oxidative (longer periods of movement, think 10k's, marathons, and beyond).

With that understanding, it makes sense that glycolytic and phosphagen-focused exercise directly improves HIIT capacity, while also giving you the benefits that HIIT provides. What may sound counter-intuitive is that performing short bursts of activity through HIIT can improve your third energy system (oxidative = endurance) that's performed in a completely different time domain.

There is growing evidence that HIIT exercise improves endurance and VO2 max, a universally accepted measure for one aspect of fitness. VO2 max refers to your body's ability to absorb and use oxygen intra-workout.

You may wonder how much HIIT you need to do for this benefit to kick in and be effective. The answer is encouraging, as the evidence shows that low-volume HIIT, involving less than 15 min of active high-intensity training per session, is a effective exercise strategy to improve cardiovascular endurance. (6)

HIIT for Building Muscle

All exercise is going to elicit a bodily response, yet the particular modality will determine the outcome of various physical components, such as fostering lean mass and developing muscle. Studies indicate that HIIT creates greater and faster adaptations (including increase in mitochondrial density) in skeletal muscle. (6)

HIIT specifically targets type II muscle fibers, and also increases ATP production up to 100 times to meet the demand of the muscle stimulus. This means that HIIT's effects downstream are inducing mitochondrial protein synthesis and mitochondrial biogenesis in the muscles. (6) Additionally, HIIT is shown to elicit comprehensive effects on overall exercise capacity and skeletal muscle metabolism. (8)

Concluding Considerations on HIIT

High-intensity interval training has been recognized as an effective exercise modality and has received substantial attention from clinical professionals. (9,10) To highlight how comprehensive these benefits of HIIT are, check out this list:

1. Improves mitochondrial biogenesis & protein synthesis in muscles
2. Improves insulin sensitivity & glucose regulation
3. Decreases total cholesterol
4. Reduces deep abdominal adiposity
5. Reduces blood pressure more than MICT (moderate-intensity continuous training)
6. Enhances skeletal muscle strength, cardiorespiratory fitness, and athletic ability

Since many of these health components are related to overall health span & longevity, it makes sense why HIIT is recommended and recognized by many as a positive adjunct to most healthy lifestyles.

Studies:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8618957

References:

1. https://www.cdc.gov/heart-disease/data-research/facts-stats/index.html#:~:text=Heart%20disease%20in%20the%20United%20States&text=One%20person%20dies%20every%2033,1%20in%20every%205%20deaths.
2. https://pubmed.ncbi.nlm.nih.gov/28051119/
3. https://pubmed.ncbi.nlm.nih.gov/32747791/
4. https://pubmed.ncbi.nlm.nih.gov/23899754/
5. https://pubmed.ncbi.nlm.nih.gov/32565243/
6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8294064
7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6763680
8. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9152764
9. https://www.nature.com/articles/s41598-023-40589-5#:~:text=HIIT%20has%20been%20recognized%20as,ability19%2C20%2C21
10. https://pubmed.ncbi.nlm.nih.gov/29511662/